The present invention relates in general to mechanisms for grasping microcomponents, and in specific to a complementary gripper and handle for grasping microcomponents.
Extraordinary advances are being made in micromechanical devices and microelectronic devices. Further, advances are being made in MicroElectroMechanical System (xe2x80x9cMEMSxe2x80x9d) devices, which comprise integrated micromechanical and microelectronic devices. The terms xe2x80x9cmicrocomponentxe2x80x9d and xe2x80x9cmicrodevicexe2x80x9d will be used herein generically to encompass microelectronic components, micromechanical components, as well as MEMs components. A need exists in the prior art for a suitable mechanism for picking and placing microcomponents. For example, a need exists for some type of xe2x80x9cgripperxe2x80x9d device that is capable of grasping a microcomponent and maintaining a rigid grasp of the microcomponent while placing the microcomponent in a desired position. For instance, such a gripper device may be included as part of a robotic device, such as a robotic arm, to allow the robotic device to perform pick and place operations with microcomponents. Such pick and place operations may be performed, for example, in assembling/arranging individual microcomponents into larger systems.
Various types of xe2x80x9cgripperxe2x80x9d mechanisms are well known for large scale components. For example, mechanisms such as tweezers, clamps, robotic hands, and a variety of other types of gripping mechanisms are well known and commonly used for gripping large scale components. However, such gripping mechanisms for large scale components are generally difficult to implement on such a small scale as necessary for gripping microcomponents. That is, many large scale gripping mechanisms are unacceptable and are not easily adaptable for use in gripping microcomponents.
Turning to FIG. 1, an example of utilizing a gripper to perform pick-and-place operations for a microcomponent is illustrated. Starting in block 10, a gripper 102 is shown, which may be utilized to pick up a microcomponent 104 and attempt to place microcomponent 104 in a desired (or xe2x80x9ctargetxe2x80x9d) location 106. In block 20, the gripper 102 approaches the microcomponent 104 in an attempt to position itself to grasp microcomponent 104. Due to the sticking effects present with such small-scale components (as discussed in more detail hereafter), microcomponent 104 may be attracted to the gripper 102 as the gripper 102 makes its approach toward microcomponent 104. Accordingly, as shown in block 20, such attraction may result in difficulty in the gripper 102 obtaining a firm grasp on the microcomponent 104. Block 30 illustrates gripper 102 having grasped microcomponent 104, and gripper 102 has picked up microcomponent 104. Thereafter, the gripper 102 may reposition the microcomponent 104, and place the microcomponent 104 on the desired location 106, as shown in block 40. Gripper 102 may then release the microcomponent 104, as shown in block 50. As further shown in block 50, however, releasing the microcomponent 104 may be difficult due to the sticking effects present with such small-scale components. Thus, microcomponent 104 may adhere to gripper 102. as the gripper 102 attempts to release the microcomponent 104, resulting in the microcomponent 104 being misaligned (or xe2x80x9cincorrectly positionedxe2x80x9d) respective to the target location 106.
As FIG. 1 demonstrates, while such pick-and-place operations initially appear to be relatively simple, when working with microcomponents, such pick and place operations are very complex. In the micro world, the relative importance of the forces that operate is very different from that in the macro world. For example, gravity is usually negligible, while surface adhesion and electrostatic forces dominate. (See e.g., A survey of sticking effects for micro parts handling, by R. S. Fearing, IEEE/RSJ Int. Workshop on Intelligent Robots and Systems, 1995; Hexsil tweezers for teleoperated microassembly, by C. G. Keller and R. T. Howe, IEEE Micro Electro Mechanical Systems Workshop, 1997, pp. 72-77; Microassembly Technologies for MEMS, by Micheal B. Cohn, Karl F. Bxc3x6hringer, J. Mark Noworolski, Angad Singh, Chris G. Keller, Ken Y. Goldberg, and Roger T. Howe; and Handbook of Industrial Robotics, by Shimon Y. Nof, chapter 5). Due to scaling effects, forces that are insignificant at the macro scale become dominant at the micro scale (and vice versa). For example, when parts to be handled are less than one millimeter in size, adhesive forces between a gripper and an object can be significant compared to gravitational forces. These adhesive forces arise primarily from surface tension, van der Waals, and electrostatic attractions and can be a fundamental limitation to handling of microcomponents. While it is possible to fabricate miniature versions of conventional robot grippers in the prior art, overcoming adhesion effects for such small-scale components has been a recognized problem.
Often in attempting to place a microcomponent in a desired location, the component will xe2x80x9cstickxe2x80x9d or adhere to the placing mechanism due to the aforementioned surface adhesion forces present in microassembly, making it very difficult to place the component in a desired location. (See e.g., Microfabricated High Aspect Ratio Silicon Flexures, Chris Keller, 1998). For example, small-scale xe2x80x9ctweezersxe2x80x9d (or other types of xe2x80x9cgrippersxe2x80x9d) may be used to perform such pick-and-place operations of microcomponents, and often such a component will adhere to the tweezers rather than the desired target location, making placing the component very difficult. It has been recognized in the prior art that to grip microcomponents and then attach them to the workpiece in the desired orientation, it is essential that a hierarchy of adhesive forces be established. For instance, electrostatic forces due to surface charges or ions in the ambient must be minimized. Adhesion of the micropart to the unclamped gripper surfaces (with zero applied force) should be less than the adhesion of the micropart to the substrate, to allow precise positioning of the part in the gripper.
Accordingly, unconventional approaches have been proposed for performing the pick-and-place operations. For example, Arai and Fukada have built manipulators with heated micro holes. See A new pick up and release method by heating for micromanipulation, by F. Arai and T. Fukada, IEEE Micro Electro Mechanical Systems Workshop, 1997, pp. 383-388). When the holes cool, they act as suction cups whose lower pressure holds appropriately shaped objects in place. Heating of the cavities increases the pressure and causes the objects to detach from the manipulator. Alternatively, some type of external adhesive (e.g., a type of liquid xe2x80x9cgluexe2x80x9d) may be utilized to enable the microcomponent to be placed in a desired location. That is, an external adhesive may be required to overcome the adhesive force between the component and the placing mechanism (e.g., tweezers). For example, the target spot on the workpiece may have a surface coating that provides sufficiently strong adhesion to exceed that between the microcomponent and the unclamped gripper.
With the advances being made in microcomponents, various attempts at developing a suitable gripper mechanism for performing pick-and-place operations have been proposed in the prior art. (See e.g., Handbook of industrial Robotics, by Shimon Y. Nof, chapter 5). However, gripper mechanisms of the prior art are problematic in that they typically do not allow for a microcomponent to be accurately positioned. One factor that commonly decreases the accuracy in the placement of a microcomponent by prior art grippers is the above-described sticking effects between the gripper and the microcomponent.
Prior art grippers commonly rely on frictional forces between the gripper and the component for performing pick-and-place operations. For example, a small-scale pair of tweezers may be utilized to squeeze against the outer edges of a component, thereby grasping the component. The pair of tweezers relies on frictional forces between the surface of the tweezers and the gripped component to prevent the gripped component from slipping out of the tweezers grasp. Prior art grippers typically grasp a component in a manner that results in a relatively large amount of surface contact between the gripper and the component. While such a large amount of surface area in contact between the gripper and the component assists the prior art grippers in maintaining a grasp on the component, it makes releasing the component very difficult because of the above-described sticking effects present.
Additionally, prior art gripper mechanisms typically do not maintain sufficient rigidity of a gripped component, as the component is being repositioned. While rigidity may be provided in one dimension by grippers of the prior art, the provided rigidity is typically insufficient in another dimension. Also, the rigidity supplied by prior art grippers is typically a result of friction between the gripper and the gripped component. Thus, a relatively large amount of surface area contact between the component and the gripper may assist in maintaining rigidity in a given dimension, but such large surface area contact results in difficulty in releasing the component because of the above-described sticking effects.
Furthermore, prior art grippers typically provide no self-alignment mechanism to aid in positioning the gripper such that it grasps the component to be picked and placed in a particular manner and/or on a particular portion of the component. For example, prior art grippers typically include no mechanism that assists the gripper during its approach to the component to allow the gripper to engage the component in an optimum fashion for picking and placing the component. For certain pick-and-place operations it may be desirable for a gripper to grasp a component on a particular portion of the component and/or in a manner such that the component has a particular orientation relative to the gripper. For example, in microassembly operations, it may be desirable to grip a component such that the component has a known orientation/position in relation to the gripper to enable the gripper to more efficiently place the component in a desired location. Additionally, it may be desirable to grasp a component on a particular portion of the component for a variety of reasons, including for the purpose of reducing the likelihood of damaging xe2x80x9csensitivexe2x80x9d portions of the component or achieving a firm grasp of the component. Given that prior art grippers typically provide no self-alignment (or positioning) mechanism with respect to a component, it is typically difficult to grasp a component in a desired fashion, particularly in view of the attractive forces commonly present between the gripper and the component during the gripper""s approach toward the component (as shown and discussed above in conjunction with block 20 of FIG. 1).
An example of one type of prior art gripper is the micro-tweezer taught by Keller in Microfabricated High Aspect Ratio Silicon Flexures. Turning to FIG. 2, micro-tweezer 200 of the prior art is shown. As shown, tweezer 200 includes arms 201 and 202, which are used to grasp a component 204 (shown as a micro-gear in FIG. 2) by applying a compression force F with arms 201 and 202 against component 204. As illustrated in FIG. 2, tweezer 200 relies not only on the compression force F to maintain a grasp on the component 204, but also relies on frictional forces between the arms 201 and 202 of the tweezer 200 and the surface of the component 204. For instance, such frictional force between the tweezer""s arms and the component are relied on to prevent the component from slipping out of the grasp of the tweezers along the Y axis of FIG. 2.
Also, the frictional force between the tweezer""s arms 201 and 202 and the component 204 aids in providing rigidity between the tweezer 200 and the component 204. Relatively firm rigidity is provided along the X axis of FIG. 2 by the grasp of the tweezer 200 on the component 204. That is, the grasp of tweezer 200 on component 204 works to prevent the component 204 from moving along the X axis relative to the tweezer 200, thereby maintaining rigidity between the tweezer 200 and the component 204 along the X axis. However, much less rigidity is present between the component 204 and the tweezer""s arms 201 and 202 along the Y and Z axes of FIG. 2. That is, much less force would be required to be applied against the component 204 to cause the component 204 to move along the Y or Z axis respective to the tweezer""s arms 201 and 202 than would be required to cause the component 204 to move along the X axis respective to the tweezer""s arms 201 and 202. More specifically, the tweezer design of FIG. 2 relies on the frictional forces between the tweezer""s arms 201 and 202 and the component 204 to provide rigidity along the Y and Z axes, which does not provide as much rigidity as provided by the actual engagement of the tweezer""s arms 201 and 202 on the component 204 along the X axis. Thus, the tweezer 200 fails to provide desirable rigidity in all three dimensions (i.e., the X, Y, and Z dimensions).
As also shown in FIG. 2, this design results in a relatively large amount of surface area contact between the component 204 and the tweezer""s arms 201 and 202. As discussed above, such surface area contact is relied on by the tweezer design in that the frictional forces between the tweezer""s arms 201 and 202 and the component 204 aid the tweezer 200 in grasping component 204. As a result, the above-described problems associated with sticking effects are prevalent in this design, causing difficulty in releasing the component 204 and accurately placing the component 204 on a target location. As can also be seen from the prior art design of FIG. 2, no aligning/positioning mechanism is provided to assist the tweezer 200 in grasping the component 204 in a desired fashion. For example, no alignment/positioning mechanism is provided to aid the tweezer 200 in grasping the component 204 on a desired portion of component 204, such as in the center of component 204. Accordingly, it may be very difficult to grasp the component 204 on a desired portion (e.g., in the center portion of component 204), and the tweezer 200 may instead achieve a grasp on a less desirable portion of component 204 (e.g., near the top or the bottom of the component 204). Additionally, no aligning/positioning mechanism is provided to aid the tweezer 200 in grasping the component 204 such that the component 204 has a particular orientation relative to the tweezer 200 once grasped. For example, the micro-gear 204 of FIG. 2 may rotate as the tweezer approaches it (due to attraction forces) making it difficult for the tweezer 200 to achieve a grasp of the micro-gear having a particular orientation relative to the tweezer 200. Given the attraction forces present on such a small-scale, the difficulty in tweezer 200 grasping the component 204 in a desired fashion is further increased.
To further assist in grasping an object with a gripper, the prior art has suggested implementing a gripper having an object-shaped cavity. (See e.g., Handbook of Industrial Robotics, by Shimon Y. Nof, Section 4.1.4). That is, the prior art has suggested implementing a gripper having a cavity that is shaped to correspond to the shape of a microcomponent to be grasped. The prior art teaches that having a cavity shaped to correspond to a component to be gripped, assists the gripper in picking up the component. Of course, such an object-shaped cavity on the gripper designed to match a first object does not match another object having a different size and/or shape. Thus, while a cavity may be shaped to conform to the size and shape of one component, it will not provide a matching cavity for components of other shapes and sizes. Thus, many grippers, each having a cavity of a different shape and size, may be required to enable one to perform pick-and-place operations with a variety of components. Furthermore, having such an object-shaped cavity implemented within a gripper does not alleviate many of the above-described problems of prior art grippers, such as the relatively large amount of surface contact between the gripper and the component, which results in difficulty in releasing and accurately placing the component on a target location.
Generally, the focus of designing prior art grippers has been on developing grippers suitable for grasping existing components. Thus, some prior art gripper designs have been directed toward gripping particular types of components, e.g., components having a particular shape and/or size. To this point, the prior art has failed to focus on adapting the components to be grasped in any manner to make such components more suitable for being gripped by a gripper. That is, prior art developments have focused solely on modifying the gripper designs to adapt to various components, without directing efforts to implement components to be more receptive or complementary of a gripper.
In view of the above, a desire exists for a gripping mechanism suitable for performing accurate pick-and-place operations with microcomponents. Also, a desire exists for a gripping mechanism that may be implemented such that a relatively small amount of surface contact is present between the gripping mechanism and the component, thereby reducing the amount of surface sticking present when releasing the component. A further desire exists for a gripping mechanism that may be implemented in a manner such that the gripping mechanism does not rely on friction between the gripping mechanism and the component to maintain rigidity therebetween, thus further allowing for ease in releasing a grasped component. Still a further desire exists for a gripping mechanism that is implemented in a manner such that it is self-aligning to a desired position on the component to be grasped, thereby allowing for the gripping mechanism to grasp the component in a desired fashion with the component having a known orientation with respect to the gripping mechanism.
These and other objects, features and technical advantages are achieved by a system and method which provide a gripping mechanism and a complementary xe2x80x9chandle,xe2x80x9d which enable a microcomponent to be grasped with the gripping mechanism. A preferred embodiment provides a gripper and a complementary handle, which is implemented on a microcomponent to be grasped, to enable the gripper to effectively grasp the microcomponent by grasping the complementary handle implemented for such component. A preferred embodiment provides a gripper and a complementary handle that is implemented on a microcomponent to enable the microcomponent to be accurately picked-and-placed with the gripper. The complementary handle may be an integrated part of the microcomponent to be grasped, or the handle may be a separate component that is capable of being permanently or temporarily coupled to a microcomponent. Most preferably, the gripper and complementary handle may be implemented to constrain all six degrees of freedom, both translational and rotational, of a grasped handle relative to the gripper. However, various implementations may constrain certain degrees of freedom of a grasped handle more or less than other degrees of freedom, relative to the gripper. Furthermore, the gripper and complementary handle may be implemented to constrain less than all six degrees of freedom of a grasped handle relative to the gripper, and any such implementation is intended to be within the scope of the present invention.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.